S. Weinbaum et al., A new view of mechanotransduction and strain amplification in cells with microvilli and cell processes, BIORHEOLOGY, 38(2-3), 2001, pp. 119-142
In this paper we shall describe new mechanical models for the deformation o
f the actin filament bundles in kidney microvilli and osteocytic cell proce
sses to see whether these cellular extensions, like the stereocilia on hair
cells in the inner ear, can function as mechanotransducers when subject to
physiological flow. In the case of kidney microvilli we show that the hydr
odynamic drag forces at the microvilli tip are <0.01 pN, but there is a 38-
fold force amplification on the actin filaments at the base of the microvil
li due to the resisting moment in its terminal web. This leads to forces th
at are more than sufficient to deform the terminal web complex of the micro
villus where ezrin has been shown to couple the actin cytoskeleton to the N
a+/H+ exchanger. In the case of bone cell processes we show that the actin
filament bundles have an effective Young's modulus that is 200 times > the
measured modulus for the actin gel in the cell body. It is, therefore, unli
kely that bone cell processes respond in vivo to fluid shear stress, as pro
posed in [59]. However, we show that the fluid drag forces on the pericellu
lar matrix which tethers the cell processes to the canalicular wall can pro
duce a 20-100 fold amplification of bone tissue strains in the actin filame
nt bundle of the cell process.